Neutrons strong nuclear force

Neutron capture always is exothermic, because the neutron is attracted to the nucleus by the strong nuclear force. Consequently, neutron capture generates a product nuclide in a metastable, excited state. These excited nuclei typically lose energy by emitting either y rays or protons ... 

In 1925 physicists had known of two particles of matter, the proton and the electron. By 1947 five were known the proton, neutron, electron, muon, and neutrino. Yet another particle, the pion, was known, but it was associated with a force and it wasn t a component of matter. In 1925 they had known of two forces gravity and electromagnetism. Now there were four. The two new ones were the weak nuclear force (now called simply the weak force ) and a strong nuclear force that held nuclei together. 

The more protons there are in a nucleus, the more neutrons are needed to help balance the repulsive electric forces. For light elements, it is sufficient to have about as many neutrons as protons. The most common isotope of carbon, carbon-12, for instance, has six protons and six neutrons. For large nuclei, more neutrons than protons are required. Remember that the strong nuclear force diminishes rapidly with increasing distance between nucleons. Nucleons must be practically touching in order for the strong nuclear force to be effective. Nucleons on opposite sides of a large atomic nucleus are not as attracted to one another. The electric force, however, does not diminish by much across the... 

All nucleons, both protons and neutrons, attract one another by the strong nuclear force. 

The presence of neutrons helps hold the atomic nucleus together by increasing the effect of the attractive strong nuclear force, represented by the single-headed arrows. 

The second reason the stabilizing effect of neutrons is limited is that any proton in the nucleus is attracted by the strong nuclear force only to adjacent protons but is electrically repelled by all other protons in the nucleus. As more and more protons are squeezed into the nucleus, the repulsive electric forces increase substantially. For example, each of the two protons in a helium nucleus feels the repulsive effect of the other. Each proton in a nucleus containing 84 protons, however, feels the repulsive effects of 83 protons The attractive nuclear force exerted by each neutron, however, extends only to its immediate neighbors. The size of the atomic nucleus is therefore limited. This in turn limits the number of possible elements in the periodic table. It is for this reason that all nuclei having more than 83 protons are radioactive. Also, the nuclei of the heaviest elements produced in the laboratory are so unstable (radioactive) that they exist for only fractions of a second. 

A brief review of the complexities to which the quark theory is addressed is in order. Particles which can interact via the strong nuclear force arc called hadrons. Hadrons can be divided into two main classes—the mesous (with baryon number zero) and the baryons (with nonzero baryon number). Within each of the classes there are small subclasses. The subclass of baryons which has been known ihe longest consists of those particles with spin j and even parity. The members of this class are the proton, the neutron, the A0 hyperon, the three hyperons and the two 3 hyperons. There are no baryons with spin 4 and even parity (or, to the usual notation, Jp = i+). The next family of baryons has ten members, each with Jp = l+. The mesons can be grouped into similar families. One of the first successes of the quark model was to explain just why there should be eight baryons with Jp = 1, ten with 1, etc., and why the various members of these families have the particular quantum numbers observed. 

A strong nuclear force carried by particles called gluons binds together protons and neutrons in an atomic nucleus. When an atom is split, energy from the atomic nucleus is released. The amount of energy released is predicted by the equation, e = me2. 

The strong nuclear force overcomes electric repulsion and holds neutrons and protons together in a nucleus. 

Every atom has an extremely dense nucleus that contains most of the atom s mass. The nucleus contains positively charged protons and neutral neutrons, both of which are referred to as nucleons. You may have wondered how protons remain in the densely packed nucleus despite the strong electrostatic repulsion forces produced by the positively charged particles. The answer is that the strong nuclear force, a force that acts only on subatomic particles that are extremely close together, overcomes the electrostatic repulsion between protons. 

To a certain degree, the stability of a nucleus can be correlated with its neu-tron-to-proton (n/p) ratio. For atoms with low atomic numbers (< 20), the most stable nuclei are those with neutron-to-proton ratios of 1 1. For example, helium ( He) has two neutrons and two protons, and a neutron-to-pro-ton ratio of 1 1. As atomic number increases, more and more neutrons are needed to produce a strong nuclear force that is sufficient to balance the electrostatic repulsion forces. Thus, the neutron-to-proton ratio for stable atoms gradually increases, reaching a maximum of approximately 1.5 1 for the largest atoms. An example of this is lead With 124 neutrons and 82... 

The strong nuclear force acts on protons and neutrons within a nucleus to hold the nucleus together. 

However, we know, from high-energy physics experiments, that the interaction potential between a neutron (of typical energy ca lO MeV) and the nucleus is not weak but involves the strong nuclear force of ca 36 MeV. We can, however, avoid the nuclear force problem by searching for a new form for the interaction potential. The required potential must give S-wave solutions to the final neutron wavefunction when the Bom approximation is applied. 

Shortly thereafter, the strong nuclear force ensured that large numbers of protons and neutrons rapidly combined to form deuterium nuclei (p + n), then helium (2p -t- 2n). The process of element building had begun. During this small niche of cosmic history, from about... 

At the start of the twenty-first century, scientists beheve that all matter is made up of tiny particles called fermions (named after American physicist Enrico Fermi). Fermions include quarks and leptons. Leptons include electrons (along with muons and neutrinos) they have no measurable size, and they are not affected by the strong nuclear force. Quarks, on the other hand, are influenced by the strong nuclear force. They are the fundamental particles that make up protons and neutrons (as well as mesons and some other particles). Both protons and neutrons are classified as baryons, composite particles each made up of three quarks. 

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